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                <h1 id="RabbitMQ笔记"><a href="#RabbitMQ笔记" class="headerlink" title="RabbitMQ笔记"></a>RabbitMQ笔记</h1><h2 id="一、MQ-的相关概念"><a href="#一、MQ-的相关概念" class="headerlink" title="一、MQ 的相关概念"></a>一、<strong>MQ</strong> <strong>的相关概念</strong></h2><h3 id="1、什么是-MQ"><a href="#1、什么是-MQ" class="headerlink" title="1、什么是 MQ"></a>1、<strong>什么是 MQ</strong></h3><p>MQ(message queue)，从字面意思上看，本质是个队列，FIFO 先入先出，只不过队列中存放的内容是message 而已，还是一种跨进程的通信机制，用于上下游传递消息。在互联网架构中，MQ 是一种非常常见的上下游“逻辑解耦+物理解耦”的消息通信服务。使用了 MQ 之后，消息发送上游只需要依赖 MQ，不用依赖其他服务</p>
<h3 id="2、为什么要用-MQ"><a href="#2、为什么要用-MQ" class="headerlink" title="2、为什么要用 MQ"></a>2、<strong>为什么要用 MQ</strong></h3><p>1.流量消峰</p>
<p>举个例子，如果订单系统最多能处理一万次订单，这个处理能力应付正常时段的下单时绰绰有余，正常时段我们下单一秒后就能返回结果。但是在高峰期，如果有两万次下单操作系统是处理不了的，只能限制订单超过一万后不允许用户下单。使用消息队列做缓冲，我们可以取消这个限制，把一秒内下的订单分散成一段时间来处理，这时有些用户可能在下单十几秒后才能收到下单成功的操作，但是比不能下单的体验要好。</p>
<p>2.应用解耦</p>
<p>以电商应用为例，应用中有订单系统、库存系统、物流系统、支付系统。用户创建订单后，如果耦合调用库存系统、物流系统、支付系统，任何一个子系统出了故障，都会造成下单操作异常。当转变成基于消息队列的方式后，系统间调用的问题会减少很多，比如物流系统因为发生故障，需要几分钟来修复。在这几分钟的时间里，物流系统要处理的内存被缓存在消息队列中，用户的下单操作可以正常完成。当物流系统恢复后，继续处理订单信息即可，中单用户感受不到物流系统的故障，提升系统的可用性。</p>
<p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220825083336874.png" alt="image-20220825083336874"></p>
<p>3.异步处理</p>
<p>有些服务间调用是异步的，例如 A 调用 B，B 需要花费很长时间执行，但是 A 需要知道 B 什么时候可以执行完，以前一般有两种方式，A 过一段时间去调用 B 的查询 api 查询。或者 A 提供一个 callback api， B 执行完之后调用 api 通知 A 服务。这两种方式都不是很优雅，使用消息总线，可以很方便解决这个问题，A 调用 B 服务后，只需要监听 B 处理完成的消息，当 B 处理完成后，会发送一条消息给 MQ，MQ 会将此消息转发给 A 服务。这样 A 服务既不用循环调用 B 的查询 api，也不用提供 callback api。同样 B 服务也不用做这些操作。A 服务还能及时的得到异步处理成功的消息</p>
<p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220825083412890.png" alt="image-20220825083412890"></p>
<h2 id="二、RabbitMQ"><a href="#二、RabbitMQ" class="headerlink" title="二、RabbitMQ"></a>二、RabbitMQ</h2><h3 id="1、关于Rabbit"><a href="#1、关于Rabbit" class="headerlink" title="1、关于Rabbit"></a><strong>1、关于Rabbit</strong></h3><p>2007 年发布，是一个在 AMQP(高级消息队列协议)基础上完成的，可复用的企业消息系统，是<strong>当前最****主流的消息中间件之一</strong>。</p>
<p>优点:由于 erlang 语言的<strong>高并发特性</strong>，性能较好；<strong>吞吐量到万级</strong>，MQ 功能比较完备,健壮、稳定、易用、跨平台、<strong>支持多种语言</strong> 如：Python、Ruby、.NET、Java、JMS、C、PHP、ActionScript、XMPP、STOMP等，支持 AJAX 文档齐全；开源提供的管理界面非常棒，用起来很好用,<strong>社区活跃度高</strong>；更新频率相当高<a target="_blank" rel="noopener" href="https://www.rabbitmq.com/news.html">https://www.rabbitmq.com/news.html</a></p>
<p>缺点：商业版需要收费,学习成本较高</p>
<h3 id="2、RabbitMQ-的概念"><a href="#2、RabbitMQ-的概念" class="headerlink" title="2、RabbitMQ 的概念"></a><strong>2、RabbitMQ 的概念</strong></h3><p>RabbitMQ 是一个消息中间件：它接受并转发消息。你可以把它当做一个快递站点，当你要发送一个包裹时，你把你的包裹放到快递站，快递员最终会把你的快递送到收件人那里，按照这种逻辑 RabbitMQ 是一个快递站，一个快递员帮你传递快件。RabbitMQ 与快递站的主要区别在于，它不处理快件而是接收，存储和转发消息数据</p>
<h3 id="3、四大核心概念"><a href="#3、四大核心概念" class="headerlink" title="3、四大核心概念"></a>3、<strong>四大核心概念</strong></h3><p><strong>生产者</strong></p>
<p>产生数据发送消息的程序是生产者</p>
<p><strong>交换机</strong></p>
<p>交换机是 RabbitMQ 非常重要的一个部件，一方面它接收来自生产者的消息，另一方面它将消息推送到队列中。交换机必须确切知道如何处理它接收到的消息，是将这些消息推送到特定队列还是推送到多个队列，亦或者是把消息丢弃，这个得有交换机类型决定</p>
<p><strong>队列</strong></p>
<p>队列是 RabbitMQ 内部使用的一种数据结构，尽管消息流经 RabbitMQ 和应用程序，但它们只能存储在队列中。队列仅受主机的内存和磁盘限制的约束，本质上是一个大的消息缓冲区。许多生产者可以将消息发送到一个队列，许多消费者可以尝试从一个队列接收数据。这就是我们使用队列的方式</p>
<p><strong>消费者</strong></p>
<p>消费与接收具有相似的含义。消费者大多时候是一个等待接收消息的程序。请注意生产者，消费者和消息中间件很多时候并不在同一机器上。同一个应用程序既可以是生产者又是可以是消费者。</p>
<h3 id="4、RabbitMQ-核心部分"><a href="#4、RabbitMQ-核心部分" class="headerlink" title="4、RabbitMQ 核心部分"></a>4、<strong>RabbitMQ 核心部分</strong></h3><p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220825083858713.png" alt="image-20220825083858713"></p>
<h3 id="5、各个名词介绍"><a href="#5、各个名词介绍" class="headerlink" title="5、各个名词介绍"></a>5、<strong>各个名词介绍</strong></h3><p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220825084033592.png" alt="image-20220825084033592"></p>
<p><strong>Broker</strong>：接收和分发消息的应用，RabbitMQ Server 就是 Message Broker</p>
<p><strong>Virtual host</strong>：出于多租户和安全因素设计的，把 AMQP 的基本组件划分到一个虚拟的分组中，类似于网络中的 namespace 概念。当多个不同的用户使用同一个 RabbitMQ server 提供的服务时，可以划分出多个 vhost，每个用户在自己的 vhost 创建 exchange／queue 等</p>
<p><strong>Connection</strong>：publisher／consumer 和 broker 之间的 TCP 连接</p>
<p><strong>Channel</strong>：如果每一次访问 RabbitMQ 都建立一个 Connection，在消息量大的时候建立 TCP Connection 的开销将是巨大的，效率也较低。Channel 是在 connection 内部建立的逻辑连接，如果应用程序支持多线程，通常每个 thread 创建单独的 channel 进行通讯，AMQP method 包含了 channel id 帮助客户端和 message broker 识别 channel，所以 channel 之间是完全隔离的。<strong>Channel 作为轻量级的****Connection</strong> <strong>极大减少了操作系统建立</strong> <strong>TCP connection</strong> <strong>的开销</strong> </p>
<p><strong>Exchange</strong>：message 到达 broker 的第一站，根据分发规则，匹配查询表中的 routing key，分发消息到 queue 中去。常用的类型有：direct (point-to-point), topic (publish-subscribe) and fanout (multicast)</p>
<p><strong>Queue</strong>：消息最终被送到这里等待 consumer 取走</p>
<p><strong>Binding</strong>：exchange 和 queue 之间的虚拟连接，binding 中可以包含 routing key，Binding 信息被保存到 exchange 中的查询表中，用于 message 的分发依据</p>
<h3 id="6、消息生产者"><a href="#6、消息生产者" class="headerlink" title="6、消息生产者"></a>6、<strong>消息生产者</strong></h3><pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Producer</span> <span class="token punctuation">{</span>
 <span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token keyword">static</span> String QUEUE_NAME <span class="token operator">=</span> <span class="token string">"hello"</span><span class="token punctuation">;</span>
 <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token keyword">throws</span> Exception <span class="token punctuation">{</span>
 <span class="token comment" spellcheck="true">//创建一个连接工厂</span>
 ConnectionFactory factory <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ConnectionFactory</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 factory<span class="token punctuation">.</span><span class="token function">setHost</span><span class="token punctuation">(</span><span class="token string">"182.92.234.71"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 factory<span class="token punctuation">.</span><span class="token function">setUsername</span><span class="token punctuation">(</span><span class="token string">"admin"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 factory<span class="token punctuation">.</span><span class="token function">setPassword</span><span class="token punctuation">(</span><span class="token string">"123"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token comment" spellcheck="true">//channel 实现了自动 close 接口 自动关闭 不需要显示关闭</span>
 <span class="token keyword">try</span><span class="token punctuation">(</span>Connection connection <span class="token operator">=</span> factory<span class="token punctuation">.</span><span class="token function">newConnection</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>Channel channel <span class="token operator">=</span> 
connection<span class="token punctuation">.</span><span class="token function">createChannel</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
 <span class="token comment" spellcheck="true">/**
 * 生成一个队列
 * 1.队列名称
 * 2.队列里面的消息是否持久化 默认消息存储在内存中
 * 3.该队列是否只供一个消费者进行消费 是否进行共享 true 可以多个消费者消费
 * 4.是否自动删除 最后一个消费者端开连接以后 该队列是否自动删除 true 自动删除
 * 5.其他参数
 */</span>
 channel<span class="token punctuation">.</span><span class="token function">queueDeclare</span><span class="token punctuation">(</span>QUEUE_NAME<span class="token punctuation">,</span><span class="token boolean">false</span><span class="token punctuation">,</span><span class="token boolean">false</span><span class="token punctuation">,</span><span class="token boolean">false</span><span class="token punctuation">,</span>null<span class="token punctuation">)</span><span class="token punctuation">;</span>
 String message<span class="token operator">=</span><span class="token string">"hello world"</span><span class="token punctuation">;</span>
 <span class="token comment" spellcheck="true">/**
 * 发送一个消息
 * 1.发送到那个交换机
 * 2.路由的 key 是哪个
 * 3.其他的参数信息
 * 4.发送消息的消息体
 */</span>
 channel<span class="token punctuation">.</span><span class="token function">basicPublish</span><span class="token punctuation">(</span><span class="token string">""</span><span class="token punctuation">,</span>QUEUE_NAME<span class="token punctuation">,</span>null<span class="token punctuation">,</span>message<span class="token punctuation">.</span><span class="token function">getBytes</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"消息发送完毕"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token punctuation">}</span>
 <span class="token punctuation">}</span> <span class="token punctuation">}</span>
</code></pre>
<h3 id="7、消息消费者"><a href="#7、消息消费者" class="headerlink" title="7、消息消费者"></a>7、<strong>消息消费者</strong></h3><pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Consumer</span> <span class="token punctuation">{</span>
 <span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token keyword">static</span> String QUEUE_NAME <span class="token operator">=</span> <span class="token string">"hello"</span><span class="token punctuation">;</span>
 <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token keyword">throws</span> Exception <span class="token punctuation">{</span>
 ConnectionFactory factory <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ConnectionFactory</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 factory<span class="token punctuation">.</span><span class="token function">setHost</span><span class="token punctuation">(</span><span class="token string">"182.92.234.71"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 factory<span class="token punctuation">.</span><span class="token function">setUsername</span><span class="token punctuation">(</span><span class="token string">"admin"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 factory<span class="token punctuation">.</span><span class="token function">setPassword</span><span class="token punctuation">(</span><span class="token string">"123"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 Connection connection <span class="token operator">=</span> factory<span class="token punctuation">.</span><span class="token function">newConnection</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 Channel channel <span class="token operator">=</span> connection<span class="token punctuation">.</span><span class="token function">createChannel</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"等待接收消息...."</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token comment" spellcheck="true">//推送的消息如何进行消费的接口回调</span>
 DeliverCallback deliverCallback<span class="token operator">=</span><span class="token punctuation">(</span>consumerTag<span class="token punctuation">,</span>delivery<span class="token punctuation">)</span><span class="token operator">-</span><span class="token operator">></span><span class="token punctuation">{</span>
 String message<span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">(</span>delivery<span class="token punctuation">.</span><span class="token function">getBody</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>message<span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token punctuation">}</span><span class="token punctuation">;</span>
 <span class="token comment" spellcheck="true">//取消消费的一个回调接口 如在消费的时候队列被删除掉了</span>
 CancelCallback cancelCallback<span class="token operator">=</span><span class="token punctuation">(</span>consumerTag<span class="token punctuation">)</span><span class="token operator">-</span><span class="token operator">></span><span class="token punctuation">{</span>
 System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"消息消费被中断"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token punctuation">}</span><span class="token punctuation">;</span>
     <span class="token comment" spellcheck="true">/**
 * 消费者消费消息
 * 1.消费哪个队列
 * 2.消费成功之后是否要自动应答 true 代表自动应答 false 手动应答
 * 3.消费者未成功消费的回调
 */</span>
 channel<span class="token punctuation">.</span><span class="token function">basicConsume</span><span class="token punctuation">(</span>QUEUE_NAME<span class="token punctuation">,</span><span class="token boolean">true</span><span class="token punctuation">,</span>deliverCallback<span class="token punctuation">,</span>cancelCallback<span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token punctuation">}</span> <span class="token punctuation">}</span>
</code></pre>
<h2 id="三、Work-Queues"><a href="#三、Work-Queues" class="headerlink" title="三、Work Queues"></a>三、<strong>Work Queues</strong></h2><h3 id="1、轮训分发消息"><a href="#1、轮训分发消息" class="headerlink" title="1、轮训分发消息"></a>1、<strong>轮训分发消息</strong></h3><p>在这个案例中我们会启动两个工作线程，一个消息发送线程，我们来看看他们两个工作线程是如何工作的。</p>
<p><strong>抽取工具类</strong> </p>
<pre class=" language-java"><code class="language-java"> <span class="token comment" spellcheck="true">//得到一个连接的 channel</span>
 <span class="token keyword">public</span> <span class="token keyword">static</span> Channel <span class="token function">getChannel</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">throws</span> Exception<span class="token punctuation">{</span>
 <span class="token comment" spellcheck="true">//创建一个连接工厂</span>
 ConnectionFactory factory <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ConnectionFactory</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 factory<span class="token punctuation">.</span><span class="token function">setHost</span><span class="token punctuation">(</span><span class="token string">"182.92.234.71"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 factory<span class="token punctuation">.</span><span class="token function">setUsername</span><span class="token punctuation">(</span><span class="token string">"admin"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 factory<span class="token punctuation">.</span><span class="token function">setPassword</span><span class="token punctuation">(</span><span class="token string">"123"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 Connection connection <span class="token operator">=</span> factory<span class="token punctuation">.</span><span class="token function">newConnection</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 Channel channel <span class="token operator">=</span> connection<span class="token punctuation">.</span><span class="token function">createChannel</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token keyword">return</span> channel<span class="token punctuation">;</span>
 <span class="token punctuation">}</span> <span class="token punctuation">}</span>
</code></pre>
<p><strong>启动两个工作线程</strong> </p>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Worker01</span> <span class="token punctuation">{</span>
 <span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token keyword">final</span> String QUEUE_NAME<span class="token operator">=</span><span class="token string">"hello"</span><span class="token punctuation">;</span>
 <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token keyword">throws</span> Exception <span class="token punctuation">{</span>
 Channel channel <span class="token operator">=</span> RabbitMqUtils<span class="token punctuation">.</span><span class="token function">getChannel</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 DeliverCallback deliverCallback<span class="token operator">=</span><span class="token punctuation">(</span>consumerTag<span class="token punctuation">,</span>delivery<span class="token punctuation">)</span><span class="token operator">-</span><span class="token operator">></span><span class="token punctuation">{</span>
 String receivedMessage <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">(</span>delivery<span class="token punctuation">.</span><span class="token function">getBody</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"接收到消息:"</span><span class="token operator">+</span>receivedMessage<span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token punctuation">}</span><span class="token punctuation">;</span>
 CancelCallback cancelCallback<span class="token operator">=</span><span class="token punctuation">(</span>consumerTag<span class="token punctuation">)</span><span class="token operator">-</span><span class="token operator">></span><span class="token punctuation">{</span>
 System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>consumerTag<span class="token operator">+</span><span class="token string">"消费者取消消费接口回调逻辑"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token punctuation">}</span><span class="token punctuation">;</span>
 System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"C2 消费者启动等待消费......"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 channel<span class="token punctuation">.</span><span class="token function">basicConsume</span><span class="token punctuation">(</span>QUEUE_NAME<span class="token punctuation">,</span><span class="token boolean">true</span><span class="token punctuation">,</span>deliverCallback<span class="token punctuation">,</span>cancelCallback<span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token punctuation">}</span> <span class="token punctuation">}</span>
</code></pre>
<p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220825084631850.png" alt="image-20220825084631850"></p>
<p><strong>启动一个发送线程</strong> </p>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Task01</span> <span class="token punctuation">{</span>
 <span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token keyword">final</span> String QUEUE_NAME<span class="token operator">=</span><span class="token string">"hello"</span><span class="token punctuation">;</span>
 <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token keyword">throws</span> Exception <span class="token punctuation">{</span>
 <span class="token keyword">try</span><span class="token punctuation">(</span>Channel channel<span class="token operator">=</span>RabbitMqUtils<span class="token punctuation">.</span><span class="token function">getChannel</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
 channel<span class="token punctuation">.</span><span class="token function">queueDeclare</span><span class="token punctuation">(</span>QUEUE_NAME<span class="token punctuation">,</span><span class="token boolean">false</span><span class="token punctuation">,</span><span class="token boolean">false</span><span class="token punctuation">,</span><span class="token boolean">false</span><span class="token punctuation">,</span>null<span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token comment" spellcheck="true">//从控制台当中接受信息</span>
 Scanner scanner <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Scanner</span><span class="token punctuation">(</span>System<span class="token punctuation">.</span>in<span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token keyword">while</span> <span class="token punctuation">(</span>scanner<span class="token punctuation">.</span><span class="token function">hasNext</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
 String message <span class="token operator">=</span> scanner<span class="token punctuation">.</span><span class="token function">next</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 channel<span class="token punctuation">.</span><span class="token function">basicPublish</span><span class="token punctuation">(</span><span class="token string">""</span><span class="token punctuation">,</span>QUEUE_NAME<span class="token punctuation">,</span>null<span class="token punctuation">,</span>message<span class="token punctuation">.</span><span class="token function">getBytes</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"发送消息完成:"</span><span class="token operator">+</span>message<span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token punctuation">}</span>
 <span class="token punctuation">}</span>
 <span class="token punctuation">}</span> <span class="token punctuation">}</span>
</code></pre>
<p><strong>结果展示</strong></p>
<p>通过程序执行发现生产者总共发送 4 个消息，消费者 1 和消费者 2 分别分得两个消息，并且是按照有序的一个接收一次消息</p>
<p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220825084729877.png" alt="image-20220825084729877"></p>
<h3 id="2、消息应答"><a href="#2、消息应答" class="headerlink" title="2、消息应答"></a>2、<strong>消息应答</strong></h3><p><strong>概念</strong> </p>
<p>消费者完成一个任务可能需要一段时间，如果其中一个消费者处理一个长的任务并仅只完成了部分突然它挂掉了，会发生什么情况。RabbitMQ 一旦向消费者传递了一条消息，便立即将该消息标记为删除。在这种情况下，突然有个消费者挂掉了，我们将丢失正在处理的消息。以及后续发送给该消费这的消息，因为它无法接收到。为了保证消息在发送过程中不丢失，rabbitmq 引入消息应答机制，消息应答就是:<strong>消费者在接****收到消息并且处理该消息之后，告诉 rabbitmq 它已经处理了，rabbitmq 可以把该消息删除了。自动应答消息发送后立即被认为已经传送成功，这种模式需要在</strong>高吞吐量和数据传输安全性方面做权<strong><strong>衡</strong>,因为这种模式如果消息在接收到之前，消费者那边出现连接或者 channel 关闭，那么消息就丢失了,当然另一方面这种模式消费者那边可以传递过载的消息，<strong>没有对传递的消息数量进行限制</strong>，当然这样有可能使得消费者这边由于接收太多还来不及处理的消息，导致这些消息的积压，最终使得内存耗尽，最终这些消费者线程被操作系统杀死，<strong>所以这种模式仅适用在消费者可以高效并</strong></strong>以某种速率能够处理这些消息的情况下使用**。</p>
<p><strong>消息应答的方法</strong> </p>
<p><strong>A</strong>.Channel.basicAck(用于肯定确认)</p>
<p>RabbitMQ 已知道该消息并且成功的处理消息，可以将其丢弃了</p>
<p><strong>B</strong>.Channel.basicNack(用于否定确认) </p>
<p><strong>C</strong>.Channel.basicReject(用于否定确认) </p>
<p>与 Channel.basicNack 相比少一个参数</p>
<p>不处理该消息了直接拒绝，可以将其丢弃了</p>
<p><strong>Multiple 的解释</strong> </p>
<p><strong>手动应答的好处是可以批量应答并且减少网络拥堵</strong></p>
<p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220825084954577.png" alt="image-20220825084954577"></p>
<p>multiple 的 true 和 false 代表不同意思</p>
<p>​	true 代表批量应答 channel 上未应答的消息</p>
<p>​		比如说 channel 上有传送 tag 的消息 5,6,7,8 当前 tag 是 8 那么此时</p>
<p>​		5-8 的这些还未应答的消息都会被确认收到消息应答</p>
<p>​	false 同上面相比</p>
<p>​		只会应答 tag=8 的消息 5,6,7 这三个消息依然不会被确认收到消息应答</p>
<p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220825085046409.png" alt="image-20220825085046409"></p>
<p><strong>消息自动重新入队</strong> </p>
<p>如果消费者由于某些原因失去连接(其通道已关闭，连接已关闭或 TCP 连接丢失)，导致消息未发送 ACK 确认，RabbitMQ 将了解到消息未完全处理，并将对其重新排队。如果此时其他消费者可以处理，它将很快将其重新分发给另一个消费者。这样，即使某个消费者偶尔死亡，也可以确保不会丢失任何消息。</p>
<p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220825085118416.png" alt="image-20220825085118416"></p>
<p><strong>消息手动应答代码</strong> </p>
<p>默认消息采用的是自动应答，所以我们要想实现消息消费过程中不丢失，需要把自动应答改为手动应答，消费者在上面代码的基础上增加下面画红色部分代码。</p>
<p><img src="https://notes-hub.oss-cn-beijing.aliyuncs.com/typora_images/image-20220825085207708.png" alt="image-20220825085207708"></p>
<p>消息生产者</p>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Task02</span> <span class="token punctuation">{</span>
 <span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token keyword">final</span> String TASK_QUEUE_NAME <span class="token operator">=</span> <span class="token string">"ack_queue"</span><span class="token punctuation">;</span>
 <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span>String<span class="token punctuation">[</span><span class="token punctuation">]</span> argv<span class="token punctuation">)</span> <span class="token keyword">throws</span> Exception <span class="token punctuation">{</span>
 <span class="token keyword">try</span> <span class="token punctuation">(</span>Channel channel <span class="token operator">=</span> RabbitMqUtils<span class="token punctuation">.</span><span class="token function">getChannel</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
 channel<span class="token punctuation">.</span><span class="token function">queueDeclare</span><span class="token punctuation">(</span>TASK_QUEUE_NAME<span class="token punctuation">,</span> <span class="token boolean">false</span><span class="token punctuation">,</span> <span class="token boolean">false</span><span class="token punctuation">,</span> <span class="token boolean">false</span><span class="token punctuation">,</span> null<span class="token punctuation">)</span><span class="token punctuation">;</span>
 Scanner sc <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Scanner</span><span class="token punctuation">(</span>System<span class="token punctuation">.</span>in<span class="token punctuation">)</span><span class="token punctuation">;</span>
 System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"请输入信息"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token keyword">while</span> <span class="token punctuation">(</span>sc<span class="token punctuation">.</span><span class="token function">hasNext</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
 String message <span class="token operator">=</span> sc<span class="token punctuation">.</span><span class="token function">nextLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  channel<span class="token punctuation">.</span><span class="token function">basicPublish</span><span class="token punctuation">(</span><span class="token string">""</span><span class="token punctuation">,</span> TASK_QUEUE_NAME<span class="token punctuation">,</span> null<span class="token punctuation">,</span> message<span class="token punctuation">.</span><span class="token function">getBytes</span><span class="token punctuation">(</span><span class="token string">"UTF-8"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"生产者发出消息"</span> <span class="token operator">+</span> message<span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token punctuation">}</span>
 <span class="token punctuation">}</span>
 <span class="token punctuation">}</span> <span class="token punctuation">}</span>
</code></pre>
<p>消费者 01</p>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Work03</span> <span class="token punctuation">{</span>
 <span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token keyword">final</span> String ACK_QUEUE_NAME<span class="token operator">=</span><span class="token string">"ack_queue"</span><span class="token punctuation">;</span>
 <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token keyword">throws</span> Exception <span class="token punctuation">{</span>
 Channel channel <span class="token operator">=</span> RabbitMqUtils<span class="token punctuation">.</span><span class="token function">getChannel</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"C1 等待接收消息处理时间较短"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token comment" spellcheck="true">//消息消费的时候如何处理消息</span>
 DeliverCallback deliverCallback<span class="token operator">=</span><span class="token punctuation">(</span>consumerTag<span class="token punctuation">,</span>delivery<span class="token punctuation">)</span><span class="token operator">-</span><span class="token operator">></span><span class="token punctuation">{</span>
 String message<span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">(</span>delivery<span class="token punctuation">.</span><span class="token function">getBody</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 SleepUtils<span class="token punctuation">.</span><span class="token function">sleep</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"接收到消息:"</span><span class="token operator">+</span>message<span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token comment" spellcheck="true">/**
 * 1.消息标记 tag
 * 2.是否批量应答未应答消息
 */</span>
 channel<span class="token punctuation">.</span><span class="token function">basicAck</span><span class="token punctuation">(</span>delivery<span class="token punctuation">.</span><span class="token function">getEnvelope</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">getDeliveryTag</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token boolean">false</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token punctuation">}</span><span class="token punctuation">;</span>
 <span class="token comment" spellcheck="true">//采用手动应答</span>
 <span class="token keyword">boolean</span> autoAck<span class="token operator">=</span><span class="token boolean">false</span><span class="token punctuation">;</span>
 channel<span class="token punctuation">.</span><span class="token function">basicConsume</span><span class="token punctuation">(</span>ACK_QUEUE_NAME<span class="token punctuation">,</span>autoAck<span class="token punctuation">,</span>deliverCallback<span class="token punctuation">,</span><span class="token punctuation">(</span>consumerTag<span class="token punctuation">)</span><span class="token operator">-</span><span class="token operator">></span><span class="token punctuation">{</span>
 System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>consumerTag<span class="token operator">+</span><span class="token string">"消费者取消消费接口回调逻辑"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token punctuation">}</span> <span class="token punctuation">}</span>
</code></pre>
<p>消费者 02</p>
<pre class=" language-java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Work04</span> <span class="token punctuation">{</span>
 <span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token keyword">final</span> String ACK_QUEUE_NAME<span class="token operator">=</span><span class="token string">"ack_queue"</span><span class="token punctuation">;</span>
 <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token keyword">throws</span> Exception <span class="token punctuation">{</span>
 Channel channel <span class="token operator">=</span> RabbitMqUtils<span class="token punctuation">.</span><span class="token function">getChannel</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"C2 等待接收消息处理时间较长"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token comment" spellcheck="true">//消息消费的时候如何处理消息</span>
 DeliverCallback deliverCallback<span class="token operator">=</span><span class="token punctuation">(</span>consumerTag<span class="token punctuation">,</span>delivery<span class="token punctuation">)</span><span class="token operator">-</span><span class="token operator">></span><span class="token punctuation">{</span>
 String message<span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">(</span>delivery<span class="token punctuation">.</span><span class="token function">getBody</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 SleepUtils<span class="token punctuation">.</span><span class="token function">sleep</span><span class="token punctuation">(</span><span class="token number">30</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"接收到消息:"</span><span class="token operator">+</span>message<span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token comment" spellcheck="true">/**
 * 1.消息标记 tag
 * 2.是否批量应答未应答消息
 */</span>
 channel<span class="token punctuation">.</span><span class="token function">basicAck</span><span class="token punctuation">(</span>delivery<span class="token punctuation">.</span><span class="token function">getEnvelope</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">getDeliveryTag</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token boolean">false</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token punctuation">}</span><span class="token punctuation">;</span>
 <span class="token comment" spellcheck="true">//采用手动应答</span>
 <span class="token keyword">boolean</span> autoAck<span class="token operator">=</span><span class="token boolean">false</span><span class="token punctuation">;</span>
 channel<span class="token punctuation">.</span><span class="token function">basicConsume</span><span class="token punctuation">(</span>ACK_QUEUE_NAME<span class="token punctuation">,</span>autoAck<span class="token punctuation">,</span>deliverCallback<span class="token punctuation">,</span><span class="token punctuation">(</span>consumerTag<span class="token punctuation">)</span><span class="token operator">-</span><span class="token operator">></span><span class="token punctuation">{</span>
 System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>consumerTag<span class="token operator">+</span><span class="token string">"消费者取消消费接口回调逻辑"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token punctuation">}</span> <span class="token punctuation">}</span>
</code></pre>
<pre class=" language-java"><code class="language-java">睡眠工具类
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">SleepUtils</span> <span class="token punctuation">{</span>
 <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">sleep</span><span class="token punctuation">(</span><span class="token keyword">int</span> second<span class="token punctuation">)</span><span class="token punctuation">{</span>
  <span class="token keyword">try</span> <span class="token punctuation">{</span>
 Thread<span class="token punctuation">.</span><span class="token function">sleep</span><span class="token punctuation">(</span><span class="token number">1000</span><span class="token operator">*</span>second<span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">InterruptedException</span> _ignored<span class="token punctuation">)</span> <span class="token punctuation">{</span>
 Thread<span class="token punctuation">.</span><span class="token function">currentThread</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">interrupt</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token punctuation">}</span>
 <span class="token punctuation">}</span> <span class="token punctuation">}</span>
</code></pre>

                
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